Fabrication of printed organic electronics (POE) is of profound interest, as such devices are ultra-low cost, are solution processable, and possess mechanical durability and structural flexibility. One type of POE, a printed thin-film transistors (TFT), has received much attention in recent years as it is a promising, low cost alternative to silicon technology for application in, for example, active-matrix liquid crystal displays (LCDs), organic light emitting diodes, e-paper, radio frequency identification tags (RFIDs), photovoltaics.
TFTs are generally composed of a supporting substrate, three electrically conductive electrodes (gate, source and drain electrodes), a channel semiconductor layer, and an electrically insulating gate dielectric layer separating the gate electrode from the semiconductor layer. It is desirable to improve the performance of known TFTs. Performance can be measured by at least two properties: mobility and the on/off ratio. Mobility is measured in units of cm2/V·sec; higher mobility is desired. The on/off ratio is the ratio between the amount of current that leaks through the TFT in the off state versus the current that runs through the TFT in the on state. Typically, a higher on/off ratio is more desirable.
Thin-film transistors (TFTs) are fundamental components in modern-age electronics, including, for example, sensors, image scanners, electronic display devices and solar cells. A solar cell is a photovoltaic device used for the conversion of solar light into electrical energy. A solar cell is usable without limitation, is environmentally friendly, unlike other energy sources, and, is thus expected to become an increasingly important energy source over time.
Conventionally, solar cells were comprised of monocrystalline or polycrystalline silicon materials. However, silicon solar cells suffer from disadvantages because they possess a high manufacturing cost and cannot be applied to a flexible substrate. One possible alternative to the silicon solar cell is a polymer solar cell.
Polymer solar cells may be manufactured through spin coating, ink-jet printing, roll coating, or doctor blading, and therefore the manufacturing process associated with a polymer solar cell is much cheaper. Further, polymer solar cells are advantageous because polymer solar cells (1) possess a large coating area, (2) have the ability to form a thin-film at low temperatures and (3) can be formed from a wide variety of substrates.
Although the polymer solar cell possesses the above advantages, it is unsuitable for practical use because the power conversion efficiency for the polymer solar cell is low (about 1%) and the polymer solar cell has a short lifetime. However, the performance of the cell has begun to greatly increase through improvements in the structural morphology of the polymer blend. Presently, in the case where the power conversion efficiency of the polymer solar cell is measured under solar light conditions, a unit device having a small area (0.1 cm2 or less) has power conversion efficiency of about 4 to about 5%, and a device having an area of 1 cm2 has power conversion efficiency of about 3%.
Despite the advances in the development of semiconducting polymers and related materials for use in photovoltaic devices, a need exists for materials and materials processing that improve the performance of these devices. The present application seeks to fulfill this need and provides further related advantages.